Water content, ash content and sulfur content are important factors for coal that influence the coal quality. In order to improving the coal quality, coal must be dehydrated and separated. With the development of technique of coal upgrading, the drying process and dry separation process for coal are widely used therein, and have obtained remarkable success.
For example, a drying equipment for coal slime has been disclosed in China patent CN 2494964Y, which is composed of a fluidized bed drying portion and a heat source supplying portion; wherein the fluidized drying portion is composed of a coal conveyor, a crusher, a pre-dryer, a screw feeder, a fluidized bed boiling dryer, a two-stage whirlwind separator, and a belt conveyor which are connected in sequence; and the heat source supplying portion is composed of a flue gas furnace, a mixer and an auxiliary assembly. In addition, a separation bed vibration device of air jigging-based dry separator has been disclosed in China patent CN 2889494Y, which comprises a vibration motor and elastic components, wherein the vibration motor is connected fixedly with the separation bed, and a rotation axis of the vibration motor is perpendicular to the screen deck of the screen plate of the separation bed; according to the working characteristic that the air jigging-based dry separation method uses the air as a media to form air jigging layers in the material to be separated, it adopts such a design for the vibration device that vibration motors with the same specification are mounted symmetrically and an output axis of the vibration motor is perpendicular to the working surface of the separation bed, which allows the vibration direction of the separation bed to be consistent with the output direction of the material, and allows the material to enter the material discharging device with shorter route during the processes of lifting up, jigging and layering of the material on the separation bed depending on the wind force, without bearing the movement for throwing the material upward on the vibration motor.
A dry separation process has been disclosed in “optimal research on coal drying system”, “Journal of china coal society”, No. 4, 2004, wherein according to the control requirement of the water content of the raw coal to be separated by the air dense medium fluidized bed dry separation method, taking gradation composition characteristic and water content distribution characteristic of coal particles with their sizes in a range from 50 mm to 6 mm into consideration, the thin layered coal moves quickly to the discharge end from feeding end on the grid plate with the effect of the vibration machine, and the hot air flow passing through the gird plate and coal layers from bottom to top exchanges considerable thermal mass with the coal particles so as to allow the free water on the coal particle surface to be evaporated quickly.
In particular, as an effective and useful technique for recrement excluding and sulfur reducing of the coal, the integrated dry separation method has been fast spread and widely used due to its unique characteristics such as saving the water source, avoiding the secondary pollution of slime water, simple process, low investment and low production cost, which are suitable for the demands of coal enterprises in China, and provides a economic and useful coal separation method for coal fabrication processing.
However, one of the major factors that influences whether the dry separation method can be used is the water content of raw coal, and the dry separation method could not be directly used due to the low separation effect thereof in the case that the outside water content of coal exceeds 9%. Further, China is rich in lignite resource, but serious in pelitization issue when coal meets water, therefore the dry separation method have to be used; however the major factors influencing the spread of dry separation method lie in the low metamorphism grade and high water content. In another aspect, the drying device needs plentiful heat source and sufficient drying time during drying the coal with high water content, and the processing ability is in inverse proportion to the dehydration strength; at present, the dehydration strength of the drying device is severely restricted to a range of 6-12% because the goal of drying device is to increase the production quantity and the calorific value only depending on drying means is limited. As a comparison, the investment and production cost of the drying device with the same scale is 3-4 times as great as that of the dry separation.
In consideration of equipment and economy, using the drying device and the dry separation device respectively leads to the dry separation method difficult to be spread due to the restriction of the raw coal quality, and difficult to be accepted by the investors due to the restriction of the large investment. There is no effective means yet to solve the problems mentioned above due to the present technique level at home or abroad.
In addition, it is well known that China is a big country of coal production and consumption, and coal occupies 75% of the primary energy constitution. A large quantity of coal is converted into electric power for supporting the national economy construction. For raw coal produced in 1997, 523 million tons among 1325 million tons are used to generate electricity, that is, coal-fired power plants consume 39.5% of national coal production quantity as the biggest coal consumers. The state that electricity generation is depending on the coal as major energy is also present in many developed countries. For example, the U.S.A. as a major country for generating electricity and producing coal, 86%-89% of the total quantity of its national coal consumption is used for power plant. Thus the foundation investment, economy operation and environment influence of the coal-fired power plant are in associated with the coal quality to a great extent. The fees for coal occupy 80% of the cost of thermal power generation. Therefore, improving the coal quality has vital influence on coal-fired power plants.
Therefore, it is desirable to provide an equipment and a method for improving coal quality which can solve the problems mentioned above and meet the requirements of country and industry for the sustainable development, environment protection and energy saving.